Although the description contained herein is directed mainly to dual fuel engines it is recognized that the described methods are applicable to other types of engines which burn a fuel having a varying energy content.
A dual fuel engine can typically operate in two modes. In a strictly liquid fuel mode a liquid fuel, such as diesel fuel, is injected directly into an engine cylinder or a precombustion chamber as the sole source of energy during combustion. In a dual fuel mode a gaseous fuel, such as natural gas, is mixed with air in an intake port of a cylinder and a small amount or pilot amount of diesel fuel is injected into the cylinder or the precombustion chamber in order to ignite the mixture of air and gaseous fuel.
A liquid fuel such as diesel fuel has a substantially constant energy content. However, the energy content of a gaseous fuel such as natural gas can vary. It is desirable that a dual fuel engine fuel control system which utilizes gaseous fuel energy content to determine the amount of gaseous fuel to deliver to the engine should be able to account for variations in the actual gaseous fuel energy content. Similarly, in a spark-ignited engine utilizing a gaseous fuel such as natural gas it may be desirable to know the actual energy content of the gaseous fuel.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.